The present invention relates to a system and method for rapid weighing of items. More particularly it relates to scale systems used in postage metering systems to weigh, and determine postage for, mailpieces or the like.
Postal scale systems are well known. Such scale systems weigh a mailpiece and determine the appropriate postage for that mailpiece as a function of the weight. Postal mailing systems where a mailpiece is transported onto a postage scale system, the appropriate postage is determined, and the mailpiece is then transported to postage metering system for imprinting with a postal indicium representative of the postage determined are also known. One such system is described in U.S. Pat. No. 4,742,878; issued May 10,1988. In such systems there is a constant need to increase the rate at which the scale can determine the weight of a mailpiece in order that the throughput of the system can be increased.
U.S. Pat. No. 4,787,048; issued: Nov. 22, 1988, discloses one approach to decreasing the time required for a postage scale system to determine the weight of a mailpiece. The system disclosed in this patent takes advantage of the structure of postage rate charts, i.e., the function that relates the weight of the mailpiece to the appropriate postage amount. Such rate charts provide a constant postage value for all weights between a pair of predetermined weight breaks. The system of the '048 patent takes advantage of this by use of an algorithm where a first estimate of the weight is made and used to determine the postage amount unless the first estimate is within a predetermined distance of a break point, in which case a second more accurate estimate is made.
A basic cause of the delay in determining weight for a mail piece is the tendency for a scale system to oscillate in response to the arrival of the mailpiece on the system. These oscillations are damped, but only slowly arrive at a new stable output value representative of the weight of the mail piece. Heretofore systems have relied on an averaging process over a number of samples taken over a number of cycles of the oscillations to approximate the weight output. While systems using such averaging type algorithms have generally proved satisfactory in the past, presently they are approaching limits such that it is difficult to increase the throughput of postage metering systems using such algorithms. One approach to increasing the speed with which weights are determined has been to develop algorithms, which determine a weight, at least to a broad approximation, from the initial transient response to a mail piece or other item arriving on a scale platform. One example of such an algorithm is commonly assigned, co-pending application Ser. No. 10/165,161, titled: SYSTEM AND METHOD FOR FAST WEIGHING OF ITEMS SUCH AS MAILPIECES; filed Jun. 7, 2002, which attempts to identify mail pieces in the first weight range (<1 oz.) from the initial response to the mail piece.
This problem is exacerbated by the presence of external (e.g. ground) vibrations, which can slow or even prevent the scale system output from converging to a sufficiently accurate approximation of the weight. One approach to the problem of external vibrations is to use sophisticated weighing algorithms that can determine a weight in the presence of external vibrations. One example of such an algorithm is commonly assigned, co-pending application Ser. No. 10/165,532; titled: SYSTEM AND METHOD FOR WEIGHING ITEMS SUCH AS MAILPIECES IN THE PRESENCE OF EXERNAL VIBRATION; filed Jun. 7, 2002. Such algorithms are complex and can be relatively slow. Further they rely on assumptions about the vibration spectrum and so may not prove effective in all cases. Still further, since they require time to identify external vibrations, they are not useful with algorithms based on the initial transient response, as discussed above.
Another approach to the problem of external vibration that has been considered by the present inventors is to separately measure the external vibration and subtract it out from the weight signal. While perhaps technically feasible, this approach has proved difficult and ultimately may prove too expensive for applications such as postal scales.
Thus it is an object of the present invention to provide a scale system, and a postage metering system incorporating such scale system, which can determine the weight of a mailpiece or the like even in an environment where periods of external vibrations which would delay or prevent convergence of the system output can occur.